A method and a circuit arrangement for regulating or controlling the current input of a consumer in an automotive vehicle is known and customary in the art, according to which a regulation or control of the actuation of a controllable switch is effected in a pulse-width modulated (PWM) regulation or control, wherein connected in series with the consumer is the controllable switch, and wherein the pulse-width modulated regulation or control of the current input of the consumer is effected by a corresponding signal being applied to the control connection of the controllable switch. The regulation or control of the current input occurs by way of the switch-on time of the controllable switch which may be configured as a field effect transistor, for example. The consumer in the automotive vehicle may e.g. be a booster, a magnetic valve, or any other consumer.
U.S. Pat. No. 4,504,779 discloses a mains supply unit wherein the speed of current variations is changed in order to overcome electromagnetic interference (EMI) problems. By means of the electronic circuit, the voltage for a consumer is controlled in that the input signal and the control voltages are controlled for a high limit and a low limit for a controllable switch. Further, DE-A-41 34 056 discloses a method for the redundant control of a current regulator.
An object of the present invention is to minimize voltage draw down in battery supply lines which are due, for example, to the switching of currents during a control operation by means of pulse-width modulation and can cause radiation of interfering signals.
This object is achieved by the present invention, wherein a circuit is used which influences the edges of a pulse-width modulated signal, in that a signal representative of the change in the current in the battery supply lines to the consumer is produced and fed back to the input signal of the circuit (negative feedback).
The emitted radiation of interfering signals is reduced by improving the current variation in the battery supply lines. It is then possible to use a much smaller electrolytic capacitor to support the batter) voltage. Further, the signal variation of the current that flows through the consumer is improved.
The resistance of the controllable switch will not change abruptly but within a certain length of time. This length of time is comparatively short and depends on the magnitude of the actuation signal. With a strong actuation signal (current or voltage), the resistance of the controllable switch changes very quickly. Current surges may then occur when switching on and off. Therefore, the intensity of the actuation signal is advantageously varied in response to the time variation of the current. Thus, the positive variation of the current is fed back to the actuation signal upon switching on so that the actuation signal is reduced. The length of time during which the controllable switch becomes conductive is therefore extended. On switching off, the negative variation of the current is fed back to the actuation signal. The decline in the actuation signal is therefore reduced. The length of time during which the controllable switch passes from the conductive condition into the non-conductive condition is therefore extended.
In a preferred embodiment, the signal representative of the current in the battery supply lines to the consumer is determined by means of a shunt resistor.
Because the current edge in the supply lines shall be regulated, a quantity derived from this current can be used for negative feedback by means of this resistor. A current measuring resistance to ground is the most inexpensive solution.
In a preferred embodiment, the consumer is an inductive consumer. In addition, a signal representative of the change in the voltage drop across the inductive consumer is fed back to the actuation signal.
When the controllable switch is switched off, the voltage edge lies in front of the current edge to be regulated and overcoming it causes overamplification of the current control. With the current edge then occurring, the control must move from overamplification back to the operating range which takes a length of time that should not be left out of account.
A preferenced circuit for implementing the method of the present invention which includes a circuit for influencing the edges of a pulse-width modulated signal, by which a signal which is representative of the change in the current in the battery supply lines to the consumer is produced and fed back to the input signal of the circuit by delivering the signal which is representative of the current in the battery supply lines to the input signal of the circuit by way of a capacitor.
It is achieved that the time variation of the signal can be sensed and fed back without a highly complex circuitry, by the employment of the capacitor.
The signal representative of the current received by the consumer is determined by means of a shunt resistor.
In a preferred embodiment, the consumer is an inductive consumer, and, in addition, a signal representative of the variation of the voltage drop across the inductive consumer is fed back to the actuation signal by delivering the signal representative of the voltage drop across the inductive consumer to the input signal of the circuit by way of a capacitor.
This has proved advantageous inasfar as no current change prevails directly upon start of a switching operation. No correction variable is fed back to the actuation signal. Thus, small current surges may occur in particular directly before switching on or off. Favorably, the variation of the voltage drop across the inductive consumer is fed back in addition. The voltage drop across the inductive consumer is basically determined by the time variation of the current according to the law of induction.
Thus, negative feedback of the time variation of the voltage drop corresponds to a negative feedback of a signal which represents the second time derivative of the current. It is thus possible to very quickly vary the actuation signal in relation to current changes.